In Sleeper, Woody Allen plays the cryogenically frozen owner of a Greenwich Village health food store who, when defrosted in the year 2173, finds himself in an authoritarian state filled with giant vegetables, android butlers, and Diane Keaton. When an unnerved Allen is first unfrozen, space-age doctors try to calm him down:

Doctor: “He’s ranting. We’d better tranquilize him.” Allen: “I knew it was too good to be true. I parked right near the hospital.” Doctor: “Here. You smoke this, and be sure to get the smoke deep down into your lungs.” Allen: “I don’t smoke. It’s tobacco.” Doctor: “It’s one of the healthiest things for your body. Now go ahead. You need all the strength you can get.”

Pointing out the always changing guidelines of salubrious living is a long-running joke in America. It’s worth remembering, though, that any self-corrections we make, and we make them all the time in real life using common sense, are far more difficult when government puts its imprimatur on pseudoscience—which it also does all the time.

In the Dietary Guidelines for Americans, the federal government’s advice manual for citizens, we are warned that “not eating breakfast has been associated with excess body weight.” But when researchers from Columbia University decided to test this notion, they found nothing of the sort: “In overweight individuals, skipping breakfast daily for 4 weeks leads to a reduction in body weight,” the study’s authors note. Other researchers did the same and came to similar conclusions. How many parents and overweight Americans took this advice as gospel when they could have been losing weight by skipping buttermilk pancake breakfasts?

We already know government recommendations regarding health are often driven by a bunch Chicken Littles. The leading organ of American scaremongering, the Centers for Disease Control and Prevention, or CDC, has gotten so much wrong over the years. There was the outrageous contention that 400,00 Americans were dropping dead from obesity every year (they weren’t). And then there were all the over-the-top warnings about the alleged risks of second-hand smoke (they don’t really exist).

Earlier this year, the bureaucrats behind the government dietary guidelines finally admitted there was “no appreciable relationship” between dietary cholesterol and blood cholesterol. After years of warning Americans that high-cholesterol foods would kill them—eggs, shrimp, and so on—the U.S. Dietary Guidelines Advisory Committee will no longer list cholesterol among its “nutrients of concern” for overconsumption. Now, some scientists argue that the state’s obsession with scaring citizens about fat may actually have made our health worse.

How did experts get it so wrong? Certainly, the food industry has muddied the waters through its lobbying. But the primary problem is that nutrition policy has long relied on a very weak kind of science: epidemiological, or “observational,” studies in which researchers follow large groups of people over many years. But even the most rigorous epidemiological studies suffer from a fundamental limitation. At best they can show only association, not causation. Epidemiological data can be used to suggest hypotheses but not to prove them.

For instance, the government has been telling us we’ve been eating too much salt for years. The Food and Drug Administration claimed that lowering salt intake would save tens of thousands of us every year. Overbearing nanny state groups lobbied the government to regulate salt like they now do trans fats, and Americans turned to low sodium diets in huge numbers.

“There is no longer any valid basis for the current salt guidelines,” said Andrew Mente, one of the authors of the study published in New England Journal of Medicine. “So why are we still scaring people about salt?”